Film bulk acoustic resonator and method for manufacturing the same

ABSTRACT

A film bulk acoustic resonator, and a method for manufacturing the same. The film bulk acoustic resonator includes a substrate, a protection layer vapor-deposited on the substrate, a membrane vapor-deposited on the protection layer and at a predetermined distance from an upper side of the substrate, and a laminated resonance part vapor-deposited on the membrane. Further, the manufacturing method includes vapor-depositing a membrane on a substrate, forming protection layers on both sides of the membrane, vapor-depositing a laminated resonance part on the membrane, and forming an air gap by removing a part of the substrate disposed between the protection layers. Accordingly, the membrane can be formed in a simple structure and without stress, and the whole manufacturing process is simplified.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Application No.2003-69838, filed Oct. 8, 2003, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an acoustic filter used in wirelesscommunication devices, and more particularly, to a film bulk acousticresonator (hereinafter, referred to as “FBAR”) which implements a highpass filter for passing only a specified high frequency component, and amethod for manufacturing the same.

2. Description of the Related Art

As mobile communication devices, such as mobile phones have becomepopular, a small and light filter for such devices has becomeincreasingly in demand. In the meantime, as a means for implementing thesmall and light filter, an FBAR has been introduced. The FBAR can beproduced in bulk at a very low cost, and manufactured in a very smallsize. In addition, the FBAR enables a high quality factor value which isa special feature of the filter, and can be used in a micro frequencyband. In particular, the FBAR is able to realize even a personalcommunication system (PCS) band and a digital cordless system (DCS)band.

In general, an FBAR element comprises a laminated resonance part createdby a first electrode, a piezoelectric layer and a second electrodevapor-deposited in the above order on a substrate. The FBAR is operatedas follows. Electric energy is applied to an electrode, and an electricfield which temporally changes is induced in the piezoelectric layer.Then, the electric field causes a bulk acoustic wave in thepiezoelectric layer in the same direction as a vibration in thelaminated resonance part, and generates the resonance.

The FBAR element includes, as shown in FIGS. 1A through 1D, a Braggreflector-type FBAR and an air gap-type FBAR.

The Bragg reflector-type FBAR of FIG. 1A is formed by vapor-depositingin order of a reflection layer 11, a lower electrode 12, a piezoelectriclayer 13, and an upper electrode 14. Here, the reflection layer 11 isformed by vapor-depositing on a substrate 10 materials having a largedifference of elastic impedance in an alternate manner. Thus-structuredBragg reflection-type FBAR elements can effectively generate theresonance since all elastic acoustic wave energy passed through thepiezoelectric layer 13 is not transferred to the substrate 10, butreflected at the reflection layer 11. The Bragg reflector-type FBAR hasa firm structure without a stress from bending, however, it is hard toform the reflection layer of at least 4 layers in precise thickness fortotal reflection. Additionally, a significant amount of manufacturingtime and a large cost are required.

On the other hand, the air gap-type FBAR uses an air gap instead of thereflection layer to separate the substrate from the resonance part, andis divided into several types according to the manufacturing methodused. Different types of air gap-type FBAR elements are illustrated inFIGS. 1B through 1D.

The FBAR element in FIG. 1B is a bulk micro-machined FBAR fabricated ina manner that a membrane 21 is formed by SiO₂, for example, on thesubstrate 20, a cavity part 23 is defined by the anisotropic etching ofa rear side of the substrate 20, and the acoustic resonator 22 is formedon the membrane 21. An FBAR element thus structured is not practical dueto its very weak structure and a low recovery rate.

The FBAR element in FIG. 1C is a surface micro-machined FBAR fabricatedas follows. A sacrifice layer (not shown) is formed on the substrate 30,and an insulation membrane 32 is formed on the sacrifice layer and thesubstrate 30. A first electrode 33, a piezoelectric layer 34 and asecond electrode 35 are vapor-deposited in order, and finally, thesacrifice layer is removed to form an air gap 31. More specifically, avia hole (not shown) is formed to connect the exterior of the element tothe sacrifice layer inside the element, and an etchant is injectedthrough the via hole to remove the sacrifice layer. Consequently, theair gap 31 is formed. Furthermore, in manufacturing the membrane, thesacrifice layer needs to be slanted, which causes a weak structure dueto a high remaining stress of the membrane.

The FBAR element of FIG. 1D is fabricated in the following manner. Acavity part 45 is defined by etching a substrate 40 using a photo-resistmembrane, and a sacrifice layer (not shown) is vapor-deposited on thecavity part 45. A membrane 41, a first electrode 42, a piezoelectriclayer 43, and a second electrode 44 are vapor-deposited in order on thesacrifice layer and the substrate 40. Then, an air gap 45 is formed byetching the sacrifice layer. In the above manufacturing method, a wetetching and a dry etching are employed in forming the air gap 45. Incase of wet etching, it is hard to remove the etchant, moreover, whenthe etchant is not completely removed, the element becomes weak due tocontinuous actions of the etchant, and the resonance frequency may bechanged. In case of dry etching, on the other hand, the etching isaccomplished by a plasmatic gas. At this time, physical impact can becaused by an ion and a molecule, and the membrane 41 or the substrate 40can be deteriorated by high temperature.

SUMMARY OF THE INVENTION

The present invention has been made to overcome the above-mentionedproblems in the related art. Accordingly, it is an aspect of the presentinvention to provide a film bulk acoustic resonator of an improveddegree of integration and a simple structure, wherein an air gap isformed by using a part of a substrate oxidized by LOCOS process for anetching stop layer, and etching a part of the other substrate, and themethod for manufacturing the same.

In order to achieve the above-described aspects of the presentinvention, there is provided a film bulk acoustic resonator comprising asubstrate, a protection layer vapor-deposited on the substrate, amembrane vapor-deposited on the protection layer and at a predetermineddistance from an upper side of the substrate, and a laminated resonancepart vapor-deposited on the membrane.

The protection layer is vapor-deposited on both sides of the substrateexcept for a predetermined part. The laminated resonance part comprisesa lower electrode vapor-deposited on the membrane, a piezoelectric layervapor-deposited on the lower electrode, and an upper electrodevapor-deposited on the piezoelectric layer.

The membrane may be a single layer of nitride, or multiple layers inwhich a nitride membrane, an oxidized membrane and the nitride membraneare sequentially vapor-deposited.

Meanwhile, a method for manufacturing a film bulk acoustic resonatoraccording to the present invention, comprises the steps ofvapor-depositing a membrane on a substrate, forming protection layers onboth sides of the membrane, vapor-depositing a laminated resonance parton the membrane, and forming an air gap by removing a part of thesubstrate disposed between the protection layers.

Here, the protection layer may be formed by a LOCOS process, and the airgap may be formed by dry etching or wet etching.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIGS. 1A to 1D are sectional views of assorted conventional film bulkacoustic resonators (FBAR);

FIG. 2 is a sectional view of an FBAR element according to an embodimentof the present invention;

FIG. 2A is a sectional view of an FBAR element according to anotherembodiment; and

FIGS. 3A to 3G show respective manufacturing processes of the FBARelement according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, a few embodiments of an FBAR element and a manufacturingmethod thereof according to the present invention will be described indetail with reference to the accompanying drawings.

As shown in FIG. 2 and FIG. 2A, the FBAR according to the presentinvention comprises a substrate 100 including an air gap 100 a, amembrane 150 vapor-deposited on the air gap 100 a to be at apredetermined distance from the substrate 100, and a laminated resonancepart 200 vapor-deposited on the membrane 150.

Except for a certain part on the top of the substrate 100, protectionlayers 110 a and 110 b are vapor-deposited. The protection layers 110 aand 110 b are formed by a localized oxidation isolation method (LOCO)process which oxidizes the substrate 100 using a mask, and functions asan etching stop layer in an etching process for forming the air gap 100a, which will be described later. The certain part on the top of thesubstrate 100, wherein the protection layers 110 a and 110 b are notvapor-deposited, is a part corresponding to the air gap 100 a. Here, theair gap 100 a isolates the substrate 100 and the laminated resonancepart 200 from each other. For the substrate 100, a silicon wafer isgenerally used.

The membrane 150 is vapor-deposited on an upper part of the air gap 100a between the protection layers 110 a and 110 b which are on thesubstrate 100. The membrane 150 supports the laminated resonance part200, and functions as an oxidation stop layer during the LOCOS process.The membrane 150 may be formed of a single layer of nitride as shown inFIG. 2. Alternatively, the membrane 150 can be formed of a multiplelayer in which a nitride membrane, an oxidized membrane and the nitridemembrane are sequentially vapor-deposited as shown in FIG. 2A.Therefore, the membrane 150 can be realized in a simple structure andwithout stress.

The laminated resonance part 200 comprises a lower electrode 210, apiezoelectric layer 220, and an upper electrode 230. The lower electrode210 is vapor-deposited on the membrane 150 and one protection layer 110a, and the piezoelectric layer 220 is vapor-deposited on the lowerelectrode 210 and the other protection layer 110 b. The upper electrode230 is vapor-deposited on the piezoelectric layer 220. In this example,the lower and the upper electrodes 210 and 230 use a general electricconductor such as a metal, to apply an electric field to thepiezoelectric layer 220. For the lower and the upper electrodes 210 and230, it is preferable to use one of Al, W, Au, Pt, Ni, Ti, Cr, Pd andMo. The piezoelectric layer 220 causes a piezoelectric effect when beingapplied with the electric field, and therefore generates an acousticwave. For the piezoelectric material, AlN, ZnO, or other material can beused. The acoustic wave generated at the piezoelectric layer 220 isreflected by the air gap 110 a, and the resonance effect is enlarged.

Hereinafter, a method for manufacturing the FBAR element according to anembodiment of the present invention will be described with reference toFIGS. 3A to 3C showing respective processes of manufacturing the FBAR.

FIGS. 3A to 3C show the process of vapor-depositing the membrane 150 andthe protection layers 110 a and 110 b on the substrate 110 using theLOCOS process. Here, the LOCOS process refers to an oxidation processselectively performed with respect to the silicon. In the LOCOS process,two areas are provided on one substrate; one area provided with anoxidation stop layer such as nitride, which can effectively preventoxygen or vapor from diffusing, and the other area not provided. A thickoxidation membrane is formed on the area wherein the oxidation stoplayer is not formed, using a difference in growth rate of thermaloxidization membrane of the two areas. The membrane 150 may be formedwith a single layer of the nitride membrane, or with a multiple layer inwhich a nitride membrane, an oxidized membrane and the nitride membraneare alternately vapor-deposited. As shown in FIG. 3C, when the oxidationprocess is applied on the substrate 100 having the membrane 150vapor-deposited, the lower part of the membrane 150 remains as it was,however, the rest of the membrane is oxidized, thereby forming theprotection layers 110 a and 110 b which are the oxidized silicon layers.

FIGS. 3D to 3G illustrate a self alignment passivation (SAP) process,and especially, FIGS. 3D to 3F show that the piezoelectric layer 200 isvapor-deposited on the membrane 150. FIG. 3D is a process of depositingthe lower electrode 210 on the membrane 150 and the one side of theprotection layer 110 a. The lower electrode 210 is vapor-deposited usinga sputtering method, an evaporation method or other methods. FIG. 3Eshows that the piezoelectric layer 220 is vapor-deposited on apredetermined part of the lower electrode 210, and the other protectionlayer 110 b. The piezoelectric layer 220 may be deposited using thesputtering or the evaporation method. FIG. 3F shows that the upperelectrode 230 is vapor-deposited on the piezoelectric layer 220. Theupper electrode 230 may be also vapor-deposited using the sputtering orthe evaporation method.

FIG. 3G shows a process of forming the air gap 100 a on the substrate100. After the piezoelectric layer 200 (FIG. 2) is vapor-deposited onthe membrane 150, the silicon substrate 100 at a lower part of themembrane 150 is etched to form the air gap 100 a. Here, a via hole (notshown) is formed before the etching process. The etching process can beperformed using wet etching or dry etching. In case of wet etching, achemical solvent such as an acetic acid aqueous solution, a hydrofluoricacid, and a phosphoric acid, is injected into the via hole to remove apart of the substrate 100. In case of dry etching, a gas, a plasma, anion beam, etc., is injected into the via hole to remove a part of thesubstrate 100, and therefore the air gap 100 a is formed.

After the air gap 100 a is formed, the FBAR having the structure in FIG.2 is completed.

Although the present invention has been described above with referenceto the FBAR element, it is not for purpose of limitation, and therefore,other various semiconductor elements using a specific layervapor-deposited on the silicon substrate can be applied.

As described above, according to the present invention, since theelement is formed on a surface of the substrate 100, the elementoccupies a minimum area, and therefore, the element has an improveddegree of integration. Furthermore, using the LOCOS process, themembrane 150 can be formed in a simple structure and without stress.

In addition, since a flattening process as in the prior art is omitted,the whole manufacturing process can be simplified. Furthermore, theLOCOS process is compatible with a CMOS process.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A film bulk acoustic resonator comprising: a substrate having twoopposite edges; a protection layer vapor-deposited on the substrate; amembrane vapor-deposited on the protection layer and spaced at apredetermined distance from an upper side of the substrate; and alaminated resonance part vapor-deposited on the membrane, wherein thelaminated resonance part comprises: a lower electrode vapor-deposited onthe membrane; a piezoelectric layer vapor-deposited on the lowerelectrode; and an upper electrode vapor-deposited on the piezoelectriclayer, wherein the protection layer is vapor-deposited on two oppositesides of the substrate except for a predetermined part defined by acavity delimited by the space between said membrane and said upper sideof said substrate, and wherein the lower electrode extends from oneopposite edge of said substrate, over said cavity, and toward one sideof the protection layer but short of said opposite edge of saidsubstrate, and the upper electrode extends from the other opposite edgeof said substrate, over said cavity and toward the other side of theprotection layer but short of said one opposite edge of said substrate.2. The film bulk acoustic resonator of claim 1, wherein the membrane isa single layer of nitride.
 3. The film bulk acoustic resonator of claim1, wherein the membrane comprises sequential layers of a nitridemembrane, an oxidized membrane and the nitride membrane.